Sulfonated polyimide ionomers: A structural study

The morphology of a series of sulfonated polyimide ionomers was investigated by small-angle X-ray and neutron scattering (SAXS and SANS) as a function of different parameters such as the ionic content, the ionic groups distribution, and the flexibility of the polymer chain. Both SAXS and SANS data exhibit the presence of an ionomer peak, indicating the presence of large ionic domains for most of the polymers. The dimension and the distribution of the ionic aggregates depend significantly on the ionic groups distribution along the polymer, and no structural evolution at nanoscopic scale accompanies the swelling process. It was found that the Dreyfus local order model where the structure of the ionic domains is locally ordered with a first four neighbors followed by a gaslike structure distribution, reproduces well our experimental data. On the other hand, the ionomer peak is not observed for very rigid polymers despite the presence of large ionic domains.